Reed muffler

ABSTRACT

A reed muffler is provided for an internal combustion engine having an exhaust duct. The muffler includes a generally circular-cylindrical housing symmetrical about an axis and defining a chamber having a tangential exhaust inlet connected to the duct and also having a central circular outlet on the axis, the outlet being defined by a short venturi section. Mounted centrally in the outlet is a generally circular reed array of about the same size as the outlet and having a number of radial reed fingers flexible to and fro from a central position, the general plane of the array being normal to the axis. The chamber usually has a fiber glass or comparable absorbent material in at least a portion of the interior. A diffuser plate is arranged parallel to the reed array on its downstream side.

[ Dec. 17, 1974 United States Patent [191 Moller 4 REED MUFFLER Primary ExaminerRichard B. Wilkinson Assistant ExaminerJohn F. Gonzales [75] Inventor: Paul S. Moller, Davis, Calif. [73] Assignee:

[221 Filed:

Attorney, Agent, or Firm-Lothropdt West Discajet Corporation, Davis, Calif. Oct. 10, 1973 ABSTRACT [211 App! 405059 A reed muffler is provided for an internal combustion x engine having an exhaust duct. The muffler includes a US. 181/58, 181/64 R symmetrical Int Cl ng a tangennd also havgenerally circular-cylindrical housing F01n 1/08 about an axisand defining a chamber havi 181/58, 40, 36 C, 35 A, tial exhaust inlet connected to the duct a [58] Field of SearcIiZIIIIII inga central circular outlet on the axis, the outlet being defined by a short venturi section. Mounted centrally in the outlet is a general] of about the same size as the out ber of radial reed fingers flexi y circular reed array References Cited UNITED STATES PATENTS I let and having a numble to and fro from a central position, the general plane of the array being normal to the axis. The chamber usuall y has a fiber m H B8 mom Wm mm Kw HP TLP m A ma am em mam MH T 23A mm HHN 0G 3o mam 29 7. 3 3

glass or comparable absorbent material in at least a portion of the interior. A diffuser plate is arranged nstream side.

6/1938 France..............

795,628 l/l936 France.;........... 590,409 7/ l 947 parallel to the reed array on its dow Great Britain..................... 181/63 3 Claims, 6 Drawing Figures VII": 1

REED, MUFFLER I In the operation of many internalrcombustion engines, particularly relativelysmall engines running on the two-stroke cycle, it is very important to provide a quiet exhaust system that is not unduly restrictive of the ing-reasons to provide a single muffler? for engines of variousdifferent sizesand work cycles, but to accomplish sound attenuati n and exhaust tuning under those conditions is difficult.

It is thereforean object of the invention to provide a reed muffler for use in'the indicated circumstances in which engine performance is satisfactory and sound is a largely reduced. I

' Another object of the invention is to provide a reed mufflerin which a relatively reed is provided.

A further object of the invention is to provide a reed muffler in which various reeds can be substituted in the muffler from-time to time to adapt the muffler to different engines and to different conditions.

inexpensive and effective r A further object of the invention is to provide a reed muffler in which, especially for two-stroke cycle engines, the muffler not only provides for exhaust quiettuning back pressure within a well defined range to provide back flow following exhaust.

In a representative instance, I provide a housing usually made up of parts that are stamped. The housing is inclusive of a back wall 8, generally a planar sheet generally circular in outline and cupped to form a circular-cylindrical side wall 9 merging with the back wall. The housing is circular cylindrical about" an axis '10, to which the back wall 8 is approximately normal.

Interconnecting the exhaust pipe 6 and the housing 7 is a transition duct 11 usually circular-cylindrical and welded to the housing 7 to enter the housing approximately on a tangential path. Gases flowing from the exhaust pipe 6 through'the transition section 11 into the housing 7 enter in a fashion substantially to swirl or retate about the axis 10. They are brought at least partly into contact with a perforated or screen wall 12 extending around at least a portion of the interiorof the chamber and assisting to confine a body 13 of fiber glass or comparable material in position.

To close one side of the chamber 7 there is provided a cover plate 14, usually a substantially circular disc having a peripheral flange 15 which is curled over an outstanding lip 16 on the wall 9 at assembly. The disc 14 has a central opening 17 which is preferably circular and is substantially symmetrical with the axis 10. The

opening is preferably defined by a short venturi section 18 formed in the cover 14 and inclusive of a curved ing but likewise affords selected exhaust back pressure.

A further object of the invention is to provide a generally improved muffler. "Other objects, together with the foregoing, are attained in the embodiment of the invention described in the accompanying description and illustrated in the accompanying drawings, in which:

j FIG. 1 is an axial cross-s'ectionthrough a typical muffler constructed pursuant to the present invention;

FIG. 2 is an elevation of one form of reed useful in connection with the muffler of FIG. 1;

fFIG. 3 is an enlarged view of the reed portion of the muffler and its immediate'e'nvironment;

' FIG. 4 is-a view similar to FIG. 3 but showing a modifiedform of reed and its environment;

FIG. 5 is a view similar to FIG. 3 but showing a further modified form of reed and its environment; and

FIG. 6 is a cross-section of the device of FIG. 5, the I there is disclosed a housing defining a chamber parf tially lined with sound absorbent material-such as fiber glass and receiving exhaust gases in an approximately tangential fashion and swirling them in towarda central axial outlet overlain by a diffuser plate.

In thepresent instance the muffler itself is of a conis arranged for attachmentto the exhaust pipe 6 of an internal combustion engine. This can be a motorcycle engine, for example, of the four-stroke cycle variety, of

the two-stroke cycle variety or of the rotary variety and is especially useful in connection with two-stroke engines for operation at high speeds, and requiring some struction comparable to that of the patent. The muffler inletv 19 and a diffuser 21 intermediate which is a throat section 22, the portion of least diameter. I Also pursuant to the invention, the opening 17 is guarded or shrouded by a'diffuser cover plate 24 having a diameter somewhat less than that of the flange 15 to afford an annular outlet 26. On the plate 24 is a number of radial embossments 27 adapted to abut the cover 14 to define a flat passage between the diffuser plate and the cover. The central portion of the diffuser is contoured to afford a cup 28 to receive a washer 29 and a bolt 31 having ahead. The bolt itself passes through a conical central portion 32 of the diffuser plate. The bolt extends through a washer 33 abutting a similar cupped portion 34 in the back wall 8, so that thebolt serves to hold the diffuser plate inposition and centralizes the diffuser plate on the main body.

Particularly pursuant to the invention, there is afforded a reed array 36. This is preferably, as shown in FIG. 2, a generally circular disc of relatively thin, spring metal having an enlarged central opening 37 therein andlikewise having a plurality of radial slots 38 formed therein to define between them an array or a number of reed fingers 39. The outer diameter of the disc. is almost exactly the same as that of the venturi throat 22, there being just sufficient clearance so that the reed can vibrate freely in the throat. The reed is assembled between the bottom of the cup portion 28 of the diffuser disc and a spacer tube 41 interposed between the reed disc and the cup portion 34 of the housing. With this arrangement, when the bolt is withdrawn, the diffuser plate can be demounted and the reed disc can likewise be withdrawn. For assembly, the reed is mounted in position and the bolt and diffuser plate are put into position, and when the nut 35 is tightened the assembly is fixed in position. vWith this construction, reed discs of difierent thicknesses and different reed fingers can be mounted in the same location in order to provide different reed characteristics for different engine tuning problems.

In the operation of this device, the exhaust gas from the pipe 6 swirls around within the housing 7, being somewhat dampened as to noise, but eventually deflects the reed disc array outwardly so that the gas can flow out into the space between the diffuser plate and the-housing and so to the atmosphere. The incoming gas from the pipe 6 travels approximately parallel to the disc 36 but finally turns and moves axially toward the disc.

- On the exhaust stroke the resulting sound wave approaches the disc 36 well before the exhaust pressure wave arrives at the reed array so that the sound wave is deflected backwardly toward the engine by the reeds when the reeds are approximately in a central position.

The redirected or inturned sound waves are again sub- 4 such as the discs'42, 43 and 44. These are generally comparable to the array 36 and are mounted in a simijected to the attenuating influence of the fiber glass or other absorbent material and are also treated acoustically in accordance with the acoustic volume and properties of the chamber.

When the exhaust gas has sufficient pressure to deflect the reed fingers or array outwardly, the sound wave has been substantially attentuated while the disc opens and permits escape of gas. The reed array, being springy, thentends to flex inwardly when the pressure gas has dissipated. The reed array then is in a position to deflect inwardly and to admit of exterior air or back .flow of some gas in the event the engine being tuned requires such back flow for its optimum work.

In flowing past the reed array, the exhaust gas does notimmediately encounter the atmosphere. Rather, it is deflected from its axial direction into a radial direction and finally escapes all around the circumferential opening 26. The gas flowing past the reed array travels at a high velocity, but the increasing passage between the housing and the diffuser disc is effective to reduce the velocity of the gas and convert some of its velocity energy into pressure energy, then assisting in the exhaust tuning operation.

With a muffler constructed as described, various discs can easily be substituted for the initial disc in order to tune the muffler for the particular engine without varying the rest of the muffler parts. Furthermore, the elastic or resilient disc is effective in the throat of the venturi to vary the flow therethrough and to act as an acoustic barrier so that the sound released to the atmosphere from the'muffier is in every instance not objectionable, and this is done without substantial detriment to or back pressure on the engine, but rather is usually done in a tuned fashion to the benefit of the engine output.

. In someinstances, as shown in FIG. 4, it is beneficial to use more than one array of reeds. The venturi throat section 22 can well receive a plurality of reed discs,

lar fashion but are, held apart axially by spacers 46, usually a distance at least sufficient so that the reed fingers in'flexing do not interfere with each other.- In this case, thefingers in each array can respond to different'frequency ranges so the muffling and tuning can cover a quite wide range of engine speeds and loads] The reed fingers need not be flat in one aspectbut can rather be of circular cross-section in a normal plane and can be used in a single, disc-like array or can be in several normal planes. As shown in FIGS. 5 and 6, the environment is the same as before including the venturi throat section 22 and the spacer 41. In this case there is provided a hub 47 from which project radially a number of round reed fingers 48 of suitable material such as metallic filaments or wires. Different disc-like finger arrays are disposed in spaced, nonnal planes by the hub 47. All reed finger arrays are similar in some cases and in others are of different diameters and stiffnesses in the different disc arrays. Also, the fingers can be relatively small in diameter and relatively large in number, virtually brush-like, to meet special muffling and tuning requirements.

In practice it has been observed that among other effects the reed arrays tend, in response to the impinging sound and pressure pulses, to vibrate in a fashion to release sound waves of higher frequencies that attenuate in shorter distances after discharge so that the atmospheric disturbance due to engine operation is restricted to a smaller atmospheric volume.

I claim:

l. A reed muffler for an internal combustion engine having an exhaust duct comprising means defining a circular-cylindrical chamber disposed about an axis, said chamber having a substantially tangent inlet connected to said duct and having an outlet, said outlet being of Venturi form and having a throat symmetrical with said axis; a plurality of flexible, radial reeds arranged in a disc-like, planar array of substantially the size of said throat; and means for mounting said array in said outlet with the plane of said array normal to said axis and substantially in said Venturi throat.

2. A device as in claim 1 including a diffuser plate connected to said chamber and overlying said array on the downstream side thereof, said diffuser being spaced away from contact with said array.

3. A device as in claim 1 in which said mounting means includes a support at the center only of said array leaving the edge of said array free to flex to and fro. 

1. A reed muffler for an internal combustion engine having an exhaust duct comprising means defining a circular-cylindrical chamber disposed about an axis, said chamber having a substantially tangent inlet connected to said duct and having an outlet, said outlet being of Venturi form and having a throat symmetrical with said axis; a plurality of flexible, radial reeds arranged in a disc-like, planar array of substantially the size of said throat; and means for mounting said array in said outlet with the plane of said array normal to said axis and substantially in said Venturi throat.
 2. A device as in claim 1 including a diffuser plate connected to said chamber and overlying said array on the downstream side thereof, said diffuser being spaced away from contact with said array.
 3. A device as in claim 1 in which said mounting means includes a support at the center only of said array leaving the edge of said array free to flex to and fro. 